Having trouble figuring out what it is.. apparently not a Coolster. No idea where model/serial number is. Thanks in advanced if you can help!

 

Unusual bike, metal filler cap, fairly chunky plastics and the most spindly, minimalist, swinging arm at the back that I have ever seen. It may have a makers plate and/or VIN behind that bull bar plastic, but do you really need to know what it is? You haven't shown the engine, but they are the most likely thing to need parts, and most small Chinese/Taiwanese bikes have either a Honda Cub, Minarelli 2stroke, or GY6 clone engine, and generic parts for these are fairly interchangeable.